Paint is generally delivered to a hand held paint spray gun from one of three sources. For large commercial applications which do not require frequent color change, the paint may be fed through a hose connected to a remote pressurized paint source. For smaller commercial and non commercial applications, the paint is generally placed in a cup attached to the gun. Most commonly, the paint cup is suspended below a front end of a body on the gun. The paint is often fed to a nozzle by suction or aspiration induced by atomization air flow through the gun. For viscous paints and for guns operating on low air pressures, the cup may be pressurized to increase the paint application rate. Finally, a paint cup is sometimes mounted above the gun body for gravity paint feed to the gun nozzle. Whether the cup is suspended below or mounted above the gun body, the cup has traditionally been mounted towards the front end of the body near the nozzle, since the paint must be delivered to the nozzle. In either case, the weight of the paint cup on the front end of the gun adversely affects the balance of the gun and may increase operator fatigue during extended use. Further, when the paint cup is secured above the front end of the gun body, it can adversely affect operator visibility during use.
Typically, when a paint cup has been mounted on the top of a hand held spray gun, it extends upwardly at an angle of at least 45.degree. relative to the spray axis about which paint is discharged. Often the angle is greater to facilitate filling the paint cup while the gun is supported on a stand. When paint is delivered from a cup by either suction or gravity feed, it is necessary to have a vent opening in the cup to allow air to enter the cup as paint is consumed. For gravity feed guns, the vent opening normally is located in the center of the cup lid as a compromise for keeping the vent opening as high as possible when spraying both vertical surfaces and the top of horizontal surfaces. A gravity feed spray gun is not suitable for spraying in an upward direction at the bottom of a horizontal surface, since the paint will not flow by gravity to the gun nozzle and paint can drip from the vent opening in the cup lid. Further, the paint feed tube will not be submerged in the paint in the cup.
When the paint cup is mounted on a hand held gun, paint leakage can be a problem when painting the top of a horizontal surface. In hand held spray guns having conventional paint cups, at least a portion of the cup lid may become submerged under the paint when coating top surfaces, such as a vehicle roof or hood, with a full paint cup. Paint can leak either from a defective lid seal or from the lid vent and drip on the workpiece during spraying horizontal surfaces where the gun is held above the surface. Surveys indicate that the most common painting problems are leaks from the cup lid seal and vent when painting top surfaces. Paint drips on the workpiece can necessitate costly repaints. In order to reduce dripping problems, prior art guns typically seal the paint cup lid either with a separate resilient gasket or with a thin resilient sealing rib. The gasket can leak because it becomes harder as paint is absorbed during use or it becomes worn from use. A thin plastic sealing rib is easily damaged. Further, both conventional cup seals will leak if not properly cleaned.
Top mounted paint cups also can present additional problems for the spray gun operator. In the prior art guns, the cup is screwed onto the top of the spray gun body. The paint cup lid is secured to the cup either by screwing the lid to the cup or by screwing a lid retainer ring to the cup. If any paint reaches the threads, the lid or the lid retainer ring may be difficult to remove. The extra force required to remove the lid may be sufficient to cause the paint cup to unscrew from the spray gun. Also, cleaning the prior art spray guns has been time consuming and expensive. For commercial operations, an expensive gun cleaner is generally required to meet environmental regulations. As much as 8 fluid ounces (0.24 liter), or more, of solvent has been required to clean a typical prior art gun and paint cup and lid. Any reduction in the amount of solvent used can reduce cleanup and solvent disposal costs and reduce potential environmental problems.